The discovery of new and more selective anticancer agents is of fundamental importance in our struggle against cancers. In 1985 the drug 5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF) was discovered by Taylor et. al. and shown to exhibit excellent antitumor activity against a broad range of tumors. It was also active against tumors that have become resistant to methotrexate (MfX), a commonly used antifolate drug used in cancer chemotherapy. DDATHF has shown some remarkable results in animal trials (complete inhibition of tumor growth at 6.25 mg/kg per day for ten days without evidence of host toxicity up to 100 mg/kg per day). The primary site of action of DDATHF has been shown to be inhibition of the enzyme glycinamide ribonucleotide formyltransferase (GARFT) which plays a critical role in de novo purine biosynthesis. The (6R) diastereomer of DDATHF, Lometrexol (LTX), is currently in clinical trials for the treatment of human neoplastic diseases. However, one study has indicated that the observed selectivity of this drug in the animal experiments was not apparent in humans and the compound was reported to show "severe toxicity". This delayed, cumulative toxicity is reported to be ameliorated if the drug is co-administered with folic acid. The overall effectiveness of the drug is, however, somewhat diminished. A thiophene analog of LTX, (LY309887; 5) discovered by Lilly Research Laboratories, has been reported to have a 3-fold greater therapeutic index compared to LTX, and has recently entered phase I clinical trials. Also, Taylor and bowling have recently reported that a pyrimidoazepine-based derivative of DDATHF (8b) shows similar antitumor properties to DDATHF, via inhibition of GARFT. We have recently reported the synthesis and antitumor activity of a one-carbon shortened side chain analog of 8b, namely 8a. In this proposal we describe our rationale and proposed method to prepare four selected pyrimidodiazepine-based analogs of DDATHF and 8b, where the stereogenic carbon in the heterocyclic ring is replaced with a nitrogen atom. Consequently, unlike DDATHF and 8b which were prepared as a mixture of two diastemmers, only one stereoisomer of the drug will be isolated alleviating the need for a laborious separation of the diastereomers at the end of the synthesis or an expensive asymmetric synthetic approach We are confident that our designed pyrimidodiazepine-based folates will show promising antitumor properties via inhibition of GARFT. We are also hopeful that at least one of our four targets will possess a better therapeutic index than LTX and LY309887.